Abstract:
Japanese encephalitis virus (JEV) is a mosquito-borne disease with potentially deadly consequences for humans and animals. Once considered a foreign threat, JEV has now been found in Australia, with outbreaks in Victoria, Queensland, and New South Wales in 2022 and 2025, which are a serious cause for concern. Using mathematical modelling, my research investigates how feral pigs could be a major contributor to maintaining JEV within Australia.
In 2022, Australia experienced a deadly outbreak of Japanese encephalitis virus (JEV), a mosquito-borne disease, which killed 6 people. Approximately 20 – 30% of people who develop encephalitis die, and 30 – 60% of survivors develop serious irreparable neurological deficits, including tremors, paralysis, and convulsions. JEV has the potential to cause widespread outbreaks affecting humans, birds, and pigs, yet the transmission of JEV within Australia is understudied. Australia has one unique environmental factor which could make JEV even more prevalent compared with the endemic regions across Southeast Asia and the Pacific: the world’s largest population of feral pigs.
But why is the presence of feral pigs so concerning?
Whilst scientists already know that pigs are a part of the natural transmission cycle, both being infected by and in turn able to produce sufficient viruses to infect mosquitos, there is also emerging evidence of direct pig-to-pig transmission. This leads to the focus of our research: could Australia’s feral pig population be contributing to the (potential) endemicity of JEV within Australia?
To answer these questions, we constructed a mathematical model to describe the transmission dynamics of JEV. This model included vector-borne transmission (via mosquitoes), and the emerging evidence of direct transmission (pig-to-pig). Then, we explored the transmission dynamics for a range of scenarios, including no pig-to-pig transmission, to better understand the transmission dynamics for JEV within Australia.
Our results show that direct transmission, if confirmed, will contribute to the endemicity of JEV. When pig-to-pig transmission was included in the model, there were more outbreaks within the pig population, and a greater proportion was infected. Without the contribution of direct transmission, over the course of ten years, the presence of JEV within the population of both species was almost non-existent. This means that feral pigs may act as an important reservoir of disease, allowing persistence of JEV year-round.
If JEV was to become established in northern Australia, where feral pig population densities are high, nomadic and semi-migratory waterbirds such as egrets and herons have the potential to spread the virus into the southern parts of the continent and internationally, increasing the risk of wide-spread outbreaks. This has implications for both the everyday Aussie, and Australian agriculture.
So, what can Australia do to prevent an outbreak? Understanding the ecology and epidemiology of JEV in Australia would be an important first step towards knowing how to best mitigate the outbreak risks.
Ultimately, disease dynamics are complex and interconnected, and understanding JEV transmission dynamics requires further studies for researchers to piece together the puzzle of the wild bird population, climate, agriculture, human health, and their effects on the endemicity of JEV within Australia.
Are feral pigs a potential viral time bomb in Australia’s backyard? The answer to this may shape Australia’s response to this emerging health threat.
Emma Naumann
James Cook University
